1. Field of the Invention
The present invention relates to a laser beam emitting apparatus using a semiconductor laser or the like and a method of driving a laser light source, and particularly to a laser beam emitting apparatus capable of controlling a laser output with efficiency and a method of driving a laser light source.
2. Description of the Related Art
A laser beam emitting apparatus using a semiconductor laser has been increasing in place of a large laser beam emitting device in recent years.
As light for a point indication or irradiating light for measurement, which is employed in surveying equipment, for example, a semiconductor laser has been used in place of a helium-neon laser emitting device and widely adopted as a battery-operable small and energy-saving light source.
In recent years in particular, a resonator-type laser beam emitting apparatus with a semiconductor laser as a pumping light source has come into being and has been employed even in a surveying device or the like.
The laser beam emitting apparatus, which has been used as the point indication light of the surveying equipment, has heretofore used a red laser beam in terms of its life, stability and economy. However, a resonator-type laser beam emitting apparatus, which emits a green laser beam with a semiconductor laser as a pumping light source, has come on the stage to further improve visibility.
The conventional laser beam emitting apparatus needs to adjust the quantity of laser light for irradiation according to surrounding light and darkness or the distance to an object or the like to be measured. The laser beam emitting apparatus has changed a current inputted to the semiconductor laser used as the pumping light source so as to adjust the quantity of the laser light to be applied.
FIG. 12 shows the relationship between an input current of a semiconductor laser and a laser output thereof. No laser beam is emitted until the input current of the semiconductor laser reaches a threshold current. When the input current of the semiconductor laser exceeds the threshold current, the laser output of the semiconductor laser rises rapidly. Thus, the light emission of the semiconductor laser needs to pass a current exceeding the threshold current in amp.
Even when the laser output is reduced, the passage of the current exceeding the threshold current in amp. through the semiconductor laser is required and the efficiency of the semiconductor laser is reduced.
In the resonator-type laser beam emitting apparatus with the semiconductor laser as the pumping light source, the current used up by the semiconductor laser increases in proportion to the square of a second harmonic generation output as shown in FIG. 13 when the current exceeding the threshold current in amp. is supplied to the semiconductor laser.
Thus, an increase or decrease in current supplied to the semiconductor laser has direct bearing on the operational efficiency of the laser beam emitting apparatus and is of extreme importance for the purpose of providing less power consumption.
Therefore, there has been a strong demand for the appearance of a laser beam emitting apparatus capable of controlling a laser beam output with high efficiency, reducing power consumption and greatly increasing a continuous service time or the like.